如何计算Ruby中的最高词频

Question

我一直在为 Rails 课程的 Coursera 介绍做这项作业。我们的任务是编写一个程序来计算文本文件中的最大词频。我们被指示创建一个方法：

计算单个单词在给定内容中出现的最大次数并存储在highest_wf_count中。
找出使用次数最多的词并将其存储在highest_wf_words。

当我运行给我们的 rspec 测试时，有一个测试失败了。我打印了我的输出以查看问题所在，但无法修复它。

这是我的代码，rspec 测试，以及我得到的结果：

class LineAnalyzer

  attr_accessor :highest_wf_count
  attr_accessor :highest_wf_words
  attr_accessor :content
  attr_accessor :line_number

  def initialize(content, line_number)
    @content = content
    @line_number = line_number
    @highest_wf_count = 0
    @highest_wf_words = highest_wf_words
    calculate_word_frequency
  end
  def calculate_word_frequency()
    @highest_wf_words = Hash.new(0)
    @content.split.each do |word|
      @highest_wf_words[word.downcase!] += 1
      if @highest_wf_words.has_key?(word)
        @highest_wf_words[word] += 1 
      else
        @highest_wf_words[word] = 1
      end
      @highest_wf_words.sort_by{|word, count| count}
      @highest_wf_count = @highest_wf_words.max_by {|word, count| count}
    end
  end
  def highest_wf_count()
    p @highest_wf_count
  end
end

这是rspec代码：

require 'rspec'

describe LineAnalyzer do
  subject(:lineAnalyzer) { LineAnalyzer.new("test", 1) }

  it "has accessor for highest_wf_count" do
    is_expected.to respond_to(:highest_wf_count) 
  end 
  it "has accessor for highest_wf_words" do
    is_expected.to respond_to(:highest_wf_words) 
  end
  it "has accessor for content" do
    is_expected.to respond_to(:content) 
  end
  it "has accessor for line_number" do
    is_expected.to respond_to(:line_number) 
  end
  it "has method calculate_word_frequency" do
    is_expected.to respond_to(:calculate_word_frequency) 
  end
  context "attributes and values" do
  it "has attributes content and line_number" do
    is_expected.to have_attributes(content: "test", line_number: 1) 
  end
  it "content attribute should have value \"test\"" do
    expect(lineAnalyzer.content).to eq("test")
  end
  it "line_number attribute should have value 1" do
    expect(lineAnalyzer.line_number).to eq(1)
  end
end

  it "calls calculate_word_frequency when created" do
    expect_any_instance_of(LineAnalyzer).to receive(:calculate_word_frequency)
    LineAnalyzer.new("", 1) 
  end

  context "#calculate_word_frequency" do
    subject(:lineAnalyzer) { LineAnalyzer.new("This is a really really really cool cool you you you", 2) }

    it "highest_wf_count value is 3" do
      expect(lineAnalyzer.highest_wf_count).to eq(3)
    end
    it "highest_wf_words will include \"really\" and \"you\"" do
      expect(lineAnalyzer.highest_wf_words).to include 'really', 'you'
    end
    it "content attribute will have value \"This is a really really really cool cool you you you\"" do
      expect(lineAnalyzer.content).to eq("This is a really really really cool cool you you you")
    end
    it "line_number attribute will have value 2" do
      expect(lineAnalyzer.line_number).to eq(2)
    end
  end
end

这是 rspec 输出：

13 examples, 1 failure

Failed examples:

rspec ./course01/module02/assignment-Calc-Max-Word-Freq/spec/line_analyzer_spec.rb:42 # LineAnalyzer#calculate_word_frequency highest_wf_count value is 3

我的输出：

#<LineAnalyzer:0x00007fc7f9018858 @content="This is a really really really cool cool you you you", @line_number=2, @highest_wf_count=[nil, 10], @highest_wf_words={"this"=>2, nil=>10, "is"=>1, "a"=>1, "really"=>3, "cool"=>2, "you"=>3}>

根据测试字符串，字数不正确。
"nil" 被包含在哈希中。
散列未按应有的值（计数）排序。

我尝试了几种方法来解决这些问题，但都没有效果。我又看了一遍讲座 material，但找不到任何有用的东西，而且讨论板上也没有经常监控学生提出的问题。

Answer 1

无:

零来自downcase!

这会就地修改字符串，如果没有任何更改，returns nil。如果你说 "this is weird"，那么你是对的（恕我直言）。

# just use the non destructive variant
word.downcase

排序:

sort_by returns 一个新对象（Hash，Array，...）并且不修改方法的接收者。您需要重新分配或使用 sort_by!

unsorted = [3, 1, 2]
sorted = unsorted.sort

p unsorted # => [3, 1, 2]
p sorted # => [1, 2, 3]

unsorted.sort!
p unsorted # => [1, 2, 3]

字数统计错误:

一旦你纠正了这两个错误，它应该看起来更好了。请注意，该方法不是 return 单个整数，而是一个包含单词和计数的双元素数组，因此它应该看起来像这样：["really", 6]

简化事情：

如果你能用ruby 2.7，那就有好用的Enumerable#tally方法了！

%w(foo foo bar foo baz foo).tally
=> {"foo"=>4, "bar"=>1, "baz"=>1}

示例取自 https://medium.com/@baweaver/ruby-2-7-enumerable-tally-a706a5fb11ea

Answer 2

根据Ruby documentation:

downcase!(*args) public

Downcases the contents of str, returning nil if no changes were made.

由于 .downcase! 方法的这种意外行为，如果单词已经全部小写，您将在该行中增加 nil 的出现次数：

@highest_wf_words[word.downcase!] += 1

测试也失败了，因为 @highest_wf_words.max_by {|word, count| count} returns 一个包含计数和单词的数组，而我们只想获取计数。

通过测试的简化 calculate_word_frequency 方法如下所示：

  def calculate_word_frequency()
    @highest_wf_words = Hash.new(0)

    @content.split.each do |word|
      # we don't have to check if the word existed before
      # because we set 0 as default value in @highest_wf_words hash

      # use .downcase instead of .downcase!
      @highest_wf_words[word.downcase] += 1

      # extract only the count, and then get the max
      @highest_wf_count = @highest_wf_words.map {|word, count| count}.max
    end
  end

如何计算Ruby中的最高词频

How to calculate the highest word frequency in Ruby

ruby

rspec

ruby-on-rails

rspec-rails